Lakes

Lakes and ponds are bodies of standing fresh water impounded in basins and depressions in the earth's continental crust. Lakes are temporary catchment basins for flowing surface and groundwater. Freshwater reservoirs form behind natural and man-made dams, surface water collects in topographic lows, and groundwater discharges into ephemeral lakes, but eventually all continental runoff drains to the ocean. Lakes provide humans with fresh drinking water, recreation areas and, in the case of the world's largest lakes, navigable waterways for ship traffic. Regional climate strongly affects the chemical and hydrological properties of lakes, and lake sediments often provide high-resolution records of climatic fluctuations. Lake basins typically fill with interlayered coarse and fine sediments, and organic material. Many ancient lacustrine deposits contain petroleum reservoirs. Because ponds, lakes, and inland seas are smaller and less well-mixed than the oceans, they are particularly susceptible to pollution.